Grapevine downy mildew is one of the major diseases in viticulture. To control this disease, a more effective strategy has been developed and established based on growth and model data as well as on a combination of fungicides. For this purpose, the systemic plant protection product potassium phosphonate (PP) was combined with two contact fungicides. Treatments were carried out according to the different experimental conditions after the growth of 400 cm², 600 cm², and 800 cm² leaf area per primary shoot. PP increased the effectiveness of the preventive fungicides whenever high infection pressure was the case. The experiments also show that it is possible to extend the treatment intervals from 400 cm² to 600 cm² new leaf area when PP was added. However, none of the tested treatments were sufficient for the extension to intervals of 800 cm². These data show that PP can be a key factor in the reduction of the application of synthetic or copper-based fungicides.

Grapevine Pinot gris virus (GPGV) was first identified in northern Italy in 2012 on grapevine variety Pinot gris showing chlorotic mottling and leaf deformation (1). Since 2012 GPGV has been reported from other countries including Slovenia, Slovakia, Czech Republic, Greece, France, Korea, United States, Canada and China. Since its discovery the association of a specific symptomology with the presence of GPGV has been contradictory. GPGV was often reported in mixed viral infections, making it difficult to associate GPGV with disease etiology. Moreover, the virus was also detected in asymptomatic vines. These observations suggest the existence of latent isolates and/or variable susceptibility of grapevine genotypes. The pathogenesis of GPGV remains unclear, therefore the studies of GPGV molecular variability and epidemiology are still of great importance. During a field survey conducted in 2015 in the state of Baden-Württemberg (Germany), symptoms resembling those caused by a viral infection (short internodes, zigzag growth of shoots, disturbed berry development) were observed in Vitis vinifera cv. Riesling vines in a commercial vineyard. Thirty vines were analyzed and were positive by RT-PCR using the GPGV- specific primer pair DetF/DetR (2). The RT-PCR amplicons from three vines were cloned and sequenced. The three amplicons were highly identical. Sequence analysis results revealed a 99% nucleotide sequence identity with the Slovak isolate SK30 of GPGV (GenBank accession number KF134123.1). Symptomatic leaves of these plants tested negative for Grapevine leafroll-associated viruses (GLRaV-1, -2, -3,- 4, and 7), Grapevine fanleaf virus, Raspberry ringspot virus, Grapevine fleck virus, Arabis mosaic virus, Strawberry latent ringspot, Tomato black ring virus, Tomato ringspot virus, Tobacco ringspot virus and Grapevine red blotch-associated virus by ELISA and/or PCR. In order to check the presence of other viral pathogens or undetected divergent viral variants, small interfering RNAs isolated from one symptomatic Riesling plant were analysed using Next Generation Sequencing (NGS) performed by the Illumina platform. Besides GPGV, this analysis identified three other infecting agents (Grapevine rupestris stem pitting-associated virus, Hop stunt viroid and Grapevine yellow speckle viroid 1). The full-length genome sequence of GPGV was obtained by combining the results of mapping of the Illumina reads on a reference GPGV genome, Sanger sequencing and RACE PCR. This genome sequence, showing 94-98% nt identity to complete genome sequences (KF686810, KF134124, KF134125, KM491305, NC _15782.1) was deposited in the GenBank database (GenBank accession number KX522755). To our knowledge, this is the first official report of GPGV in Germany.

Grapevine downy mildew, evoked by the obligate biotrophic oomycete Plasmopara viticola, is one of the most challenging diseases in viticulture. P. viticola establishes an infection by circumvention of plant immunity, which is achieved by the secretion of effector molecules. One family of potential effectors are the necrosis- and ethylene-inducing peptide 1 (Nep1)-like proteins (NLP). NLP are most abundant in plant pathogenic microorganisms and exist in cytotoxic and non-cyctotoxic forms. Cytotoxic NLP often act as virulence factors and are synthesized in necrotrophic or hemibiotrophic pathogens during the transition from biotrophic to necrotrophic growth. In addition to these cytotoxic NLP, many non-cytotoxic NLP have been identified; their function in biotrophic pathogens is still unknown. In 2020, eight different NLP coding genes were identified in P. viticola and named PvNLP1 to PvNLP8 (Plasmopara viticolaNLP 1–8). In the present study, PvNLP4 to PvNLP8 were characterized by using qPCR analysis and transient expression in the model plant Nicotiana benthamiana. Gene expression analysis showed high PvNLP expression during the early stages of infection. Necrosis-inducing activity of PvNLP was not observed in the nonhost N. benthamiana.

Viral diseases in viticulture lead to annual losses in the quantity and quality of grape production. Since no direct control measures are available in practice, preventive measures are taken to keep the vines healthy. These include, for example, the testing of propagation material for viruses such as Arabis mosaic virus (ArMV), Grapevine fanleaf virus (GFLV) or Grapevine leafroll-associated virus 1 (GLRaV-1) and 3 (GLRaV-3). As long-term investigations have shown, GLRaV-1 (2.1%) occurs most frequently in southwestern German wine-growing regions, whereas GLRaV-3 (<0.1%) is almost never found. However, tests conducted over 12 years indicate that there is no general decline in virus-infected planting material. Thus, it can be assumed that a spread of the viruses via corresponding vectors still takes place unhindered. Beyond the examinations regulated within the German Wine Growing Ordinance, one-time tests were carried out on Grapevine Pinot gris virus (GPGV). This analysis showed that GPGV was found in 17.2% of the samples.

Control of downy mildew on grapevines in organic viticulture in Europe is mainly based on using copper-based fungicides. However, the effect of these agents is often insufficient to prevent losses when infestation pressure is high. The addition of sulfur, which is primarily used to control powdery mildew, improves the effect of copper on downy mildew. In three out of five trial years, sulfur had a clear positive effect when it was added during spray treatments against Plasmopara viticola, the causal agent of downy mildew on grapevines. This was evident mainly in the fruits; no further positive effect on the leaves was evident. In addition, the present study shows that copper-based fungicides are effective on leaves but have a rather poor effect on grapevine fruit. Furthermore, the study demonstrates that the effect of copper is significantly worse than that of the chemical synthetic contact fungicide folpet.

Resistance of grapevine against powdery mildew (Erysiphe necator) and downy mildew (Plasmopara viticola) increases during ontogenetic development of leaves and berries. The aim of this study was to determine whether the use of fungicides against both pathogens could be reduced during the last treatment before harvest (LTBH) by treating only the susceptible leaves of the vines in the upper half of the canopy. For this purpose, field trials were carried out under experimental or practical conditions in vineyards in southern Germany in eight different years. All plants were sprayed after a standard regimen until LTBH, performed at BBCH 77–79. LTBH was either performed on the whole canopy or limited to the upper half of the canopy excluding the fruit zone. For both pathogens, no differences were observed between the two treatments with regard to the disease severity on the grape clusters. Only in one out of eight years, an increased fruit disease incidence could be observed. As far as the disease severity of leaves is concerned, no differences were observed for downy mildew, and in the case of powdery mildew, significantly higher infestation was observed only in two out of eight years. Furthermore, the efficacy of different fungicides for LTBH was investigated in a 3-year experiment. Sole use of a copper fungicide for LTBH had no disadvantages against E. necator, compared to a treatment with synthetic fungicides. Taken together, LTBH at BBCH 77–79 can be limited to the upper canopy without risk to the health of the fruit.